The present invention relates to a material shredder, especially for crushing sugar cane. Such shredders have a hammer rotor rotatably supported in the housing. The rotor cooperates with an anvil yieldably mounted in the housing.
The ever increasing mechanization of the harvesting of sugar cane makes it practically unavoidable that stones and sometimes even metal parts are supplied into the shredder along with the sugar cane. As a result, the hammers of the rotor and the respective anvil members are subjected to heavy wear and tear and quite frequently damages are not avoidable.
Such disadvantages are due to the fact that in a number of conventional shredders, the anvil is merely adjustable relative to the rotor but the anvil is not able to yield relative to the rotor when relatively hard extraneous matter enter into the working gap between the hammers of the rotor and the anvil. German Patent Publication (DAS) 1,782,530 and U.S. Pat. Nos. 3,248,263, as well as 3,351,295 describe shredders of the just mentioned type.
British Pat. No. 462,128 describes a shredder having a rotor with knives cooperating with counter knives secured to the anvil. The anvil is journaled to a lever system at its end facing toward the material inlet. The opposite end of the anvil is tiltable about an axis extending in parallel to the rotor axis. The rotor axis and the journal axis of the anvil cannot yield relative to each other. In other words, the spacing between the rotor axis and the anvil journal axis is constant. A tension spring is effective on the anvil through the lever system in such a manner that the anvil is pressed toward the rotor. Due to this arrangement, the anvil and its knives are able to evade extraneous bodies at the beginning of the working gap between the anvil and the rotor adjacent to the material inlet since the anvil end adjacent to the material inlet can be deflected against the biasing spring action. Howver, the opposite end of the anvil cannot yield. Therefore, the interacting knives are subject to extremely heavy wear and tear or even destruction when extraneous matter or bodies pass through the working gap.
U.S. Pat. No. 1,864,973 discloses a rock crusher constructed as a shredder. The anvil is arranged relative to the rotor in such a manner that the working gap tapers in the direction of the material throughput. The anvil end at the material outlet is subjected to the bias of a spring which presses the anvil towards the rotor. Thus, the anvil is able to yield radially around a tilting axis located at its opposite end namely the end adjacent to the inlet. Disregarding for the moment that a wedge shaped tapered working gap is not suitable for shredding sugar can or similar material, the use of this type of structure for the anvil support in a sugar can shredder would not avoid the above described disadvantages of the prior art because the springs acting on the anvil in a substantially radially effective direction resist a radial deflection of the anvil by extraneous matter in the working gap in such a manner that, depending on the type of spring characteristic, the spring resistance to yielding of the anvil exhibits a steep rise in response to an increasing deflection. As a result, any extraneous matter must pass the elements which interact in a cutting manner at an extremely increased working pressure. This type of anvil yielding might, at best, somewhat reduce the wear and tear, however, it is not possible to reliably avoid the destruction of the cutting edges in this type of apparatus.
In connection with garbage shredders, it is very likely that metal parts or other resisting and bulky matters enter into the working gap. Therefore, it is conventional to construct the anvil in such garbage shredders in such a manner that the anvil or parts thereof may yield resiliently. First, German Pat. No. 1,104,301 discloses, for example, a shredder provided with a row of spring biased individual tearing teeth. However, the effective direction of the spring forces extends substantially radially relative to the rotational axis of the rotor. The individual tearing teeth serving as cutting elements of the anvil are not able to prepare sugar cane in a manner necessary for the processing following the shredding. Further, this type of structure has the disadvantage that, depending on the type of spring characteristic, the resistance offered by the tearing teeth against any deflection rises steeply as large radial deflections are required. Stated differently, the tearing teeth offer a higher resistance against extraneous bodies in the material to be shredded than against the material to be shredded. Another garbage shredder which is disclosed in German Patent Publication (DAS) 2,034,074 as well as in the German Utility Model 7,025,833, comprises a rotor suspended at its both ends by means of two parallel guide rods of equal lengths. The guide rods are operatively secured to the housing, whereby the rotor, the housing, and the guide rods form a parallelogram. The guide rods which support the anvil at the inlet for the material to be shredded is adjustable in its length by means of an adjustable spindle, whereby the size of the working gap between the rotor and the anvil may be selected. However, rubber springs are provided as part of the adjusting spindle, whereby the anvil is able to swing about its normal position, thereby deforming the rubber springs. Due to the arrangement of the guide rod parallelogram, the anvil can yield only in such a manner that it is moved away from the rotor uniformly along its entire length. Such a feature is undesirable in a sugar cane shredder because it would cause an unsatisfactory shredding since a substantial proportion of the sugar cane would leave the shredder without having been sufficiently shredded. Further, this type of lever or rod support of the anvil also does not provide a reliable protection of the shredding elements against an increased loading. This is so because the rubber springs in the adjustment spindles also have a characteristic with a very steep rise of the spring resistance, whereby a heavy wear and tear or a destruction of the anvil cutting edges or of the hammers cannot be avoided. In view of the above it will be noted that neither the known shredders for sugar cane nor the garbage shredders of the prior art which operate in the manner of hammer mills, provide any suggestion how to avoid excessive loads on the interacting crushing elements.